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DEPARTMENT OF COMMERCE 



Technologic Papers 



OF THE 



Bureau of Standards 

S. W. STRATTON, Director 



No. 160 

EFFECTS OF OILS, GREASES, AND DEGREE OF 

TANNAGE ON THE PHYSICAL PROPERTIES 

OF RUSSET HARNESS LEATHER 

BY 

R. C. BOWKER, Assistant Mechanical Engineer 

Bureau of Standards 

in cooperation with 

J. B. CHURCHILL, Director 

American Leather Research Laboratory 



Aprii 17,1920 



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PRICE, S CENTS 



Sold only by the Superintendent of Documents, Government Printing Office 
Washington, D. C. 



WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1920 



Monograph 



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EFFECTS OF OILS, GREASES, AND DEGREE OF TAN- 
NAGE ON THE PHYSICAL PROPERTIES OF RUSSET 
HARNESS LEATHER 



By R. C. Bowker and J. B. Churchill 



CONTENTS 

Page 

I. Introduction 3 

II. Methods 4 

1. Selection of the leather 4 

(a) Description of the leather selected 4 

(6) Preparation of samples 6 

2. Physical tests 7 

(a) Tensile strength 7 

(£) Stretch 7 

(c) Buckle strength 8 

3. Chemical tests 8 

(a) Stuffing content 8 

(b) Complete analysis 8 

III. Data and results obtained 9 

1 . Physical tests 9 

(a) Tensile strength 9 

(6) Stretch 12 

(c) Buckle strength 13 

2. Chemical tests 14 

(a) Stuffing content 14 

(b) Complete analysis 15 

3. Comparison of physical and chemical tests 16 

(a) Effect of the amount of stuffing content on the physical 

properties 16 

(b) Effect of the degree of tannage on the physical properties. . 17 

(c) Effect of animal and mineral oils on the physical properties- 18 

IV. Conclusions 18 

I. INTRODUCTION 

During the war physical and chemical tests of the equipment 
leather purchased by the War Department were made at the 
Bureau for the purpose of controlling the quality of the leather 
furnished by the various tanneries. An opportunity was thus 
offered for a study of the variations in the physical properties 
and in the chemical constituents of many kinds of leather. On 
account of the large quantities used the values of the various 

3 



4 Technologic Papers of the Bureau of Standards 

properties for both russet and black harness leathers were of special 
interest. Russet harness leather is not a regular commercial 
product in this country and finds little use except for military 
purposes. Black harness leather, however, is a regular commer- 
cial product and is widely used. Besides the difference in color, 
there are three distinct differences between these two leathers 
caused by the process of manufacture. The first of these differ- 
ences occurs in the length of the tanning operation. It is general 
practice to give hides for black harness leather a short-time 
tannage, while those for russet harness leather are tanned for a 
longer time. The average degree of tannage as determined from 
the chemical analyses of black and russet harness leathers made 
during the war were 46 and 61, respectively. The second point 
of difference between these two kinds of leather is shown by the 
amount of stuffing used. The average amounts found in the 
above-mentioned black and russet leathers were 29.3 and 15.5, 
respectively. The third difference is caused by the general prac- 
tice of adding to black harness leather small amounts of such filling 
materials as glucose and salts. This procedure is not generally 
followed in the case of russet harness leather. A better selection 
of hides is generally used for the latter leather, since the coloring 
of black harness readily conceals many surface imperfections 
which do not affect the quality. In order to study more definitely 
the effects of the amount and kind of stuffing content and also the 
degree of tannage on the physical properties of harness leather, 
this investigation was made. 

II. METHODS 

1. SELECTION OF THE LEATHER 

Russet harness leather was used in this investigation. Three 
hides were prepared, marked butt Nos. 1,2, and 3, to study the 
effects of different amounts of stuffing content, of animal and 
mineral oils, and of medium and heavy tannage, respectively, on 
the physical properties. 

The method of using whole hides or double backs in preparing 
this leather was used, so that, when split, each single back could 
be given its special finishing treatment and when tests were made 
the leather of the two sides compared would come from the same 
hide. Each side was given a code letter. 

(a) Description op The Leather Selected. — The hides from 
which the leather was produced were treated in the usual manner, 



Harness Leather 



which consisted of soaking, fleshing, liming, unhairing, handling, 
and then laying away in the yard. The tanning materials used 
were liquors made from chestnut-oak bark, chestnut wood, and 
quebracho. After the tanning was completed the hides were 
split, shaved, scoured, and bleached with a solution of soda and 
water, sulphuric acid and water, and sumac and water. The 
leather was then stuffed and later oiled. The finishing was done 
by hand. 

Butt No. /.— This hide received the regular tannage for this type 
of leather and, after being split, one side (B) was stuffed with a 
mixture of cod oil and tallow, using the amount ordinarily used 
in the particular tannery where the leather was made. The other 











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Fig. i. — Division of a side into blocks 

side (A) was stuffed with a larger amount of the mixture, equal 
approximately to that used by some tanners of black harness 
leather. These two sides were used to study the effects of different 
amounts of stuffing content on the physical properties. 

Butt No. 2. — The leather produced by this hide was used to 
study the effects of a medium and heavy tannage on the physical 
properties. The hide, after receiving the regular tanning treat- 
ment, was split and one side (C) removed, while the other side 
(D) was allowed to remain in the vats a month longer in order to 
receive a heavier tannage. 

Butt No. 3. — This hide, after being tanned as regular russet 
harness leather, was split and one side {E) was stuffed with a 
mixture of 50 per cent cod oil and 50 per cent tallow. The other 
side (F) was stuffed with a mixture of 50 per cent Breton mineral 
oil and 50 per cent tallow. This leather was prepared to deter- 
mine, if possible, the effects of the use of mineral and animal oils 
on the physical properties of leather. 



Technologic Papers of the Bureau of Standards 



(b) Preparation op Samples. — Each side of leather was di- 
vided into 40 blocks, as shown in Fig. 1 , beginning at the butt end, 
near the root of the tail, with block No. 1 and running across the 
hide from back to belly. The blocks running from the butt end 
to the shoulder end were numbered in steps of four. The size of 
each block was approximately 8 inches in length and 7 inches in 
width. Each was divided into samples for the various tests, as 



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Fig. 2. — Division of a block into samples for the different tests 

shown in Fig. 2. Three samples from each block, designated by 
Ti, T2, and T3, were prepared for the tensile strength and elon- 
gation tests, and three samples, designated by Bi, B2, and B3, 
were used for the buckle tests. That part of each block used for 
the chemical tests is designated by the letter C. Each sample 
cut from any block carried the code letter of the bend, the number 
of the block, and the letter representing the test for which the 
sample was to be used. 



Harness Leather 



2. PHYSICAL TESTS 



The physical tests generally made on samples of harness leather 
for determining the quality are for tensile strength and percentage 
elongation. In addition, a buckle or shearing test was made. 

(a) Tensile Strength. — This is the test most commonly made, 
the results being expressed in pounds per square inch. Test 
pieces were cut with a metal die from each individual strip. The 
shape and size of the resulting sample are shown in Fig. 3. The 
ends are enlarged and the central portion is reduced to a width 
of one-half inch over a gage length of 2 inches. This shape usually 
insures that the sample will break within the reduced section and 
prevents tearing in the grips of the testing machine. The break- 
ing strength, in pounds, of each sample was determined with a 
tension machine the jaws of which separated at a rate of approx- 




Fig. 3. — Shape and size of tensile strength specimens 

imately 6 inches per minute. With this value and the area, as 
determined by the width and thickness of the reduced section, the 
tensile strength in pounds per square inch was calculated. 

The breaking strength, in pounds per inch of width, was also 
determined. There were three values for each of these properties 
for each block and an average of the three for each property was 
used as representing the value for the particular location on the 
side indicated by the block number. 

(6) Stretch. — The stretch, or percentage elongation, of each 
tension test piece was determined at the breaking strength. The 
method consisted of first marking on the reduced section parallel 
lines 2 inches apart. A convenient method of noting the stretch, 
used in this test, consisted of following the parallel lines on the 
test pieces, as they separated under the tension, with a pair of 
dividers. The elongation was then measured with a scale and the 
percentage increase calculated. In this case also the average of 
three values represented the value for the block. 



8 Technologic Papers of the Bureau of Standards 

(c) Buckle Strength. — There are many parts of a harness 
which are used in conjunction with a buckle. It is common 
knowledge that the failure oi a particular strap or part of a har- 
ness often occurs at one of the holes through which the tongue 
of the buckle passes. It was thought desirable to study the 
variation on the hide in the buckle or shearing strength of new 
harness leather with the idea in view of showing what portions 
of the hide might be most suitable for those straps which are 
used with a buckle. Three samples for this test were prepared 
from each block, as shown in Fig. 4. A hole of the proper size 
for the buckle tongue was punched 1 inch from the end of the 
test piece. An ordinary i>£-mch harness buckle with a tongue 
approximately eighteen-hundredths of an inch in diameter was 
secured to a strap which was placed in one jaw of the testing 




Fig. 4. — Shape and she of buckle strength specimens 

machine. The punched end of the test piece was then inserted 
in the buckle and the free end secured in the other jaw of the 
machine. The number of pounds required to pull the test piece 
through the buckle was then noted. 

3. CHEMICAL TESTS 

(a) Stuffing Content. — It was considered possible that the 
variation in the amount of stuffing content over the hide might 
have some effect on the physical properties. For this reason, 
and also to study the distribution of the stuffing content over the 
hide, a chemical determination was made of this property for 
each block of each side. 

(b) Complete Analysis. — In order to aid in the interpretation 
of the physical results, and also to have all the data possible for the 
identification of the several sides, a complete chemical analysis 
was made of each, using a composite sample prepared by taking 
an equal quantity from each block. 



Harness Leather g 

III. DATA AND RESULTS OBTAINED 
1. PHYSICAL TESTS 

(a) Tensile Strength. — The results of the tensile-strength 
tests, expressed in pounds per square inch, are shown graphically 
in Figs. 5,6, and 7. Each individual curve of the graphs represents 

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Fig. 5. — Variation of tensile strength in pounds per square inch over the side for samples 

A and B 

the values obtained from four blocks running from the backbone 
edge to the belly edge. The values for the tensile strength, in 
pounds per inch of width, are shown graphically in Figs. 8,9, and 
10. For that portion of any side represented by blocks 1 to 28, 
inclusive, the strength is generally greater on the backbone edge, 
decreasing in value toward a point near the belly edge, beyond 



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Fig. 6. — Variation of tensile strength in pounds Per square inch over the side for samples 

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which it generally increases to either an equal or greater value 
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162023°— 20—2 



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Technologic Papers of the Bureau of Standards 



and to decrease steadily to the belly edge. A glance at Figs 8, 
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Fig. 7. — Variation of tensile strength in pounds per square inch over the side for samples 

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where it is lowest, and then slightly increasing in value again for 
the remaining two sections. This same variation applies to the 
values for tensile strength, in pounds per square inch, but is not 
so marked, due to the fact that the thickness is variable, which 
greatly affects these values. As an illustration, considering 
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and B in tensile strength in pounds per square inch. Fig. 8 shows 




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Fig. 8. — Variation of tensile strength in pounds per inch of width over tlie side for samples 

A and B 

the values of the tensile strength, in pounds per inch of width, for 
these two sides, and it will be noted that there is not such a 
marked difference between the values as in the case of Fig. 5. 
The difference shown in Fig. 5 is due to the fact that the average 
thickness over the side was greater for one than for the other. 



Harness Leather 



ii 



Thus, it is conceivable that the products of two different tanners 
might have equal strength per inch of width, but due to the 
different methods used the thickness of one tanner's leather might 
be considerably less or greater than that of the other tanner, and 
the results would be that, although the amount of fiber substance 
was the same, the tensile strength as expressed in pounds per 






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square inch would be quite different for the two leathers. The 
functions of the various parts of a harness are to withstand a 
definite strain or pull in tension which depends more upon the 
strength of the leather per inch of width than upon the strength 
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Fig. 10. — Variation of tensile strength in pounds per inch of width over the side for samples 

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to do. In view of these facts, it would seem desirable for specifi- 
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The graphs show that there is a great variation in the strength 
in pounds per square inch over the hide, and for this reason it is 
difficult to set a standard value. The generally accepted require- 
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Technologic Papers of the Bureau of Standards 



the choice, although in the two butt-end sections of all the sides 
the value is somewhat less. The results also show that the strength 
of the more open texture, looser, long-fibered belly and shoulder 
portions is equal to or greater than the strength of any other 







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Fig. ii. — Variation in, per cent stretch over the side for samples A and B 

portions of the side. The quality of the leather from these por- 
tions, however, is inferior to the more closely fibered and firmer 
area extending approximately 1 5 inches on either side of the back- 



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Fig. 12. — Variation in per cent stretch over the side for samples C and D 

bone. Thus it will be seen that high tensile strength alone does 
not insure the best quality of leather. 

(b) Stretch. — The results of the stretch tests are shown graphi- 
cally in Figs, ii, 12, and 13. The value of this property was 








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lowest along the backbone edge of the sides and increased toward 
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on the extreme belly edge. An interesting fact regarding the 
stretch shows that in many cases it increases when the strength is 



Harness Leather 



13 



low and decreases when it is high. This does not occur in propor- 
tion to the difference in strength, but is clearly shown by the fact 
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Fig. 14. — Variation in buckle strength' over the side for samples A and B 

(c) Buckle Strength. — The results of the buckle strength 
tests are shown graphically in Figs. 14, 15, and 16. It will be 
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Fig. 15. — Variation in buckle strength over the side for samples C and D 

belly edge, after which it decreases to a minimum at the belly edge 
for any section of four blocks running across the bend. The aver- 
age value for the buckle strength for any section is greatest in the 
butt end and decreases steadily to the shoulder end. 






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Locution On Ttts Jies 

Fig. 16. — Variation in buckle strength over the side for samples E and F 

An effort was made to establish a percentage relation between 
the buckle strength and tensile strength per inch of width. This 
relation was subject to a variation of from 10 to 50 per cent in 
one side, so that no satisfactory figure could be accepted as stand- 
ard. The results, however, show that the belly and shoulder pro- 



14 



Technologic Papers of the Bureau of Standards 



tions are inferior to the remaining portion of the side for use in 
straps which are to be used with a buckle. The best portion of a 
hide for this purpose, as shown by these tests, would be that in- 
cluded in an area about 1 5 inches either side of the backbone and 
30 inches in length from the root of the tail. This test would 
not be of much value when examining samples of sides for general 
use as harness leather, but would be valuable in testing a lot of 
straps cut for use with a buckle. Table 1 gives the average values 
resulting from the tests. 



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Fig. 17. — Variation of stuffing content over the side for samples A and B 

TABLE 1.— Average Values for Thickness, Tensile Strength, Percentage Stretch 
and Buckle Strength for each Side 





Side 


Thickness, 
inches 


Tensile strength 


Per- 
centage 
stretch 


Buckle 
strength, 
pounds 


Butt 


Pounds 
per inch 
ol width 


Founds 

per square 

Inch 


1 


A 
B 
C 
D 

E 
F 


0.196 
.178 
.180 
.198 
.175 
.172 


740 
806 
865 
810 
815 
795 


3835 
4600 
4920 
4130 
4705 
4605 


30.8 
29.0 
31.6 
31.1 
28.3 
28.2 


201 


1 


195 


2 


170 


2 


205 


3 


163 


3 


180 







2. CHEMICAL TESTS 

(a) Stuffing Content. — The values for the amount of stuffing 
content found in each block are shown graphically in Figs. 17, 
18, and 19. The average amount for any section is least at the 



Harness Leather 



15 



butt end and then gradually increases to the shoulder, where 
the stuffing content is greatest. The general tendency is for the 
stuffing content to be greatest in the more open belly and shoulder 
portions. In the case of all except bend .4 the average stuffing 



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Fig. i8. — Variation of stuffing content over the side for samples C and D 

content runs from 10 to 15 per cent and is shown to be fairly 
evenly distributed over the side, except in the shoulder. When 
a larger amount of stuffing was used, as in the case of bend A, 
the distribution over the hide was less uniform, and the greater 








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Fig. 19. — Var»a<ton of stuffing content over the side for samples E and F 

part of the stuffing was absorbed by the belly and shoulder por- 
tions of the hide. 

(b) Complete Analysis. — A complete chemical analysis was 
made of each side, and the results are given in Table 2. 



1 6 Technologic Papers of the Bureau of Standards 

TABLE 2. — Results of Complete Chemical Analyses for all Sides 

[Calculated to 10 per cent moisture] 





Butt No. 1 


Butt No. 2 


Butt No. 3 




Side A 


SideB 


Side C 


SideD 


Side E 


SideF 




10.00 
.32 
.23 
23.35 
32.74 
10.05 
2.06 
7.99 

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23.74 
72.51 

.50 


10.00 

.27 

.23 

10.70 

39.92 

10.20 

2.07 

8.13 

w 

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29.03 
72 73 

.52 


10.00 

.43 

.21 

13.30 

40.24 

9.88 

2.58 

7.30 

(«) 

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26.44 

65.71 

.35 


10.00 

.35 

.22 

11.46 

39.81 

10.66 

2.16 

a so 

(o) 

.14 
27.93 
70.16 

.32 


10.00 

.31 

.23 

13.72 

37.32 

10.92 

2.27 

8.65 

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27.90 
74.93 

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36.10 




9.77 




2.20 




7.57 




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78.12 


Acidity 


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a None. & Degree of tannage is in each case calculated from the figures given in corresponding table. 
3. COMPARISON OF PHYSICAL AND CHEMICAL TESTS 

(a) Effect of the Amount of Stuffing Content on the 
Physical Properties. — The two sides A and B from the same 
hide were prepared to show the effect of different amounts of 
stuffing content on the physical properties. Side A contained 
23.35 per cent of grease, while side B contained 10.70 per cent. 
It is apparent from Fig. 5 that side A, which contains the higher 
percentage of grease , is uniformly lower in tensile strength expressed 
in pounds per square inch than is side B. The average difference 
in strength is nearly 20 per cent and since the two sides are as 
nearly equal in quality in every respect, except grease content, 
as is possible to obtain it might be assumed that the difference in 
strength is caused by the different grease contents. The higher 
stuffing content in side A, however, caused another effect that 
must be considered, which was to increase materially the thickness 
of the side so that its average thickness throughout was 10 per 
cent greater than that of side B. Hence the cross-sectional areas 
of the various test pieces were greater for side A than for side B. 
This fact, assuming that the same breaking load would be obtained 
for test pieces from the same relative location on each side, would 
cause one test piece from side A to have a lower strength per unit 
of cross section. Thus, it would appear that about one-half, or 
10 per cent, of the difference in strength indicated in Fig. 5 is 
due to the difference in thickness of the two sides which was caused 
by the different stuffing contents. The remaining 10 per cent 



Harness Leather 17 

difference in strength may be attributed directly to the grease 
content. 

In the case of the tensile strength in pounds per inch of width 
(Fig. 8) side B has an average value 9 per cent greater than that 
of side A. Since the tensile strength per square inch for side B 
was 20 per cent greater than that for side A, half of which was 
apparently caused by the difference in thickness of the two sides, 
the remaining 10 per cent can be attributed to the difference of 
the two sides in the strength per inch of width. The strength in 
pounds per inch of width is a more nearly true indication of the 
comparative strength of different leathers, since it does not take 
into account the thickness, which might vary for leathers on 
account of any difference in the methods of tanning and finishing 
by different manufacturers, and expresses the result for the same 
amount of original hide substance regardless of the treatment of 
the hide. 

The effect of the grease content on the stretch was not appreci- 
able, and the difference between the average values for the two 
sides was only about 3 per cent. 

There did not appear to be any appreciable effect, because of the 
grease content, on the buckle strength. The difference between 
the average values for the two sides was about 3 per cent. 

It can not be definitely stated from the results of these tests 
whether the variation in the grease content over the hide has any 
effect on the strength. It is more likely that any effect produced 
by the variation is secondary to the effect on the strength caused 
by the location on the hide from which a sample is taken. 

(b) Effect of the Degree of Tannage on the Physical 
Properties. — Sides C and D were prepared for this test. Side D 
was tanned the longer time, but the analysis of both show that 
side C had reached that stage in the tanning process beyond which 
the increase in the degree of tannage is slow. This is shown by 
the fact that the difference in the degree of tannage figures for 
the two sides was approximately 5. 

The tensile strength in pounds per square inch (Fig. 6) for side C 
was uniformly greater throughout than for side D. This result 
is what would be expected, since side C, having the lighter tannage, 
was relatively nearer to the raw-hide condition in which condition 
the strength would be greatest. The average strength, in pounds 
per square inch, for side C was approximately 20 per cent greater 
than for side D, but, as was the case with sides A and B, side D 
was also 10 per cent thicker than side C, thus causing its average 



1 8 Technologic Papers of the Bureau of Standards 

tensile strength in pounds per square inch to be considerably less 
for the same amount of original hide. The average strength per 
inch of width for side C was 7 per cent greater than for side D. 
Although the degree of tannage values for these two sides was not 
very different, it would appear that the lower strength of side D 
is due to the longer time in the tanning process. 

The stretch of the leather did not appear to be materially 
affected by the different lengths of tannage, the average value 
for the stretch being nearly the same in both cases. 

The average buckle strength for side D (Fig. 15) was approxi- 
mately 20 per cent greater than the value for side C. Thus, it 
would appear that a long-time tannage would produce a more 
solid and firmer leather, which would resist a shearing action to 
a greater degree than a leather tanned for a shorter period of time. 

(c) Effect of Animal and Mineral Oils on the Physical 

Properties. — Sides E and F were prepared for this test. The 

average tensile-strength and stretch values were nearly the same 

for both sides, but the average buckle strength of side F was 

approximately 10 per cent greater than the average value for 

side E. This may be on account of the fact that, although both 

sides were tanned for the same length of time, side F had a higher 

value for the degree of tannage. The results indicate that there 

is no essential effect upon the physical properties of new leather 

caused by the use of mineral instead of animal oils in the stuffing 

content. 

IV. CONCLUSIONS 

Although this investigation was somewhat limited in its scope, 
the following general conclusions have been drawn, based upon the 
results obtained with the material used in these experiments: 

1. That the amount of stuffing content affects the tensile 
strength of the leather and that there is a point beyond which 
the amount of stuffing content used does not add to the strength 
and may actually serve to decrease it. 

2. That the tensile strength is greater for leather tanned a 
short time than for leather given a long-time tannage, and that 
the degree of tannage also affects the- firmness of the leather, the 
longer-time tannage producing leather more resistant to shear when 
used with a buckle. 

3. That the use of the type of mineral oil with which side F 
was stuffed does not affect the physical properties of new leather 
in a manner different than that caused by the use of cod oil. 

Washington, October 27, 1919. 



LIBRARY OF CONGRESS 



015 992 294 7 









LIBRARY OF CONGRESS 




015 992 294 7 m 



Hollinger Corp. 
P H 8.5 



